Simulator development is already a huge burden for many academic and industry research groups; future complex or heterogeneous multi-cores, as well as the multiplicity of performance metrics and required functionality, will make matters worse. We present a new simulation environment, called UNISIM, which is designed to rationalize simulator development by making it possible and efficient to distribute the overall effort over multiple research groups, even without direct cooperation. UNISIM achieves this goal with a combination of modular software development, distributed communication protocols, multi-level abstract modeling, interoperability capabilities, a set of simulator services APIs, and an open library/repository for providing a consistent set of simulator modules.